Various types of tillage tool arrangements have been developed to prepare fields for planting. A type of such tools is referred to as one-pass tillage tools not because a seedbed can be completely prepared in a single pass over the field, but because several operations are performed in a one pass, reducing the number of passes across the field and thereby saving time and energy. The operations typically performed are discing, chemical application and incorporation for weed control, cultivating, and a harrowing operation. Discing cuts through and buries residue, such as, stalks, roots, and the like, from a previous crop. The discs help to level the soil to some degree by reducing ridges and filling in furrows. Discs also turn and mix the soil which is desirable when applying and incorporating chemicals in front of the discs. Discs offer these advantages over a straight coulter gang, which only cuts through residue. Typical discs are dished or concave, while coulters are flattened or planar.
A typical one-pass tool includes a single row of discs, which may be angled with an inner end of the gang positioned forward or rearward of the outer end, or a combination of alternately angled disc gangs. A problem that arises from a single row of discs is that the discs tend to move the soil laterally which can create ridges and furrows. The ridging and furrowing problem can be compounded when multiple passes are made in the same field. One solution is to add a second row of discs angled oppositely from the first to counteract the soil ridging and furrowing actions of the first disc gang. Such an arrangement is referred to as a tandem disc harrow. However, the addition of a second disc gang adds significant cost to the arrangement, requires lengthened frame members to accommodate the second disc gang and heavier lift axles for the increased weight, and increases the horsepower required to pull the tool frame. A second row of discs will also tend to bury more residue which may not be desired in some farming operations.
Other measures are taken to limit soil movement and minimize ridging. The discs used are relatively small, about eighteen to twenty inches in diameter and usually of low concavity. The disc angle is relatively low, commonly eight to ten degrees from lateral. Discing depth is limited by spring loaded gangs. Greater speeds of the discs through the soil increase the tendency toward ridging. However, slowing down from a conventional six to eight miles per hour to four miles per hour is not always feasible. These measures help to reduce ridging, but do not completely eliminate the problem.
Soil or spray shields used for chemical incorporation are sometimes mounted behind disc gangs to limit soil movement. Such shields can be mounted rigidly or allowed to swing. If shields are rigidly mounted close enough to the disc gangs to limit lateral soil movement, they tend to plug and can severely disrupt the flow of soil from the disc gangs. On the other hand, shields which are mounted for swinging are generally ineffective in preventing lateral soil movement behind disc gangs at normal working speeds.
Thus, there is a need for a tool or other means which prevents, counteracts, or otherwise compensates for the tendency of disc gangs to form ridges and furrows due to lateral movement of soil. Such a tool should work effectively behind single rows of discs and should work in a variety of soil conditions, moisture contents, and residues, and at a variety of working speeds.